The present invention relates to an improved speedometer/odometer apparatus, and more particularly to a speedometer/odometer apparatus which is able to more accurately display the speed/mileage.
In the applicant's U.S. Pat. No. 5,105,150, a wide-band programmable tachometer and speedometer/odometer apparatus of a vehicle is disclosed, wherein a mechanical motion of an engine is first converted into an electronic signal. Then the electronic signal is amplified and sent to a frequency divider 4 and then through a multiplexer 5. A selecting switch 7 is incorporated with the multiplexer 5 to send out a signal with frequency in an operable range. An F-V converter 6 is used to convert the signal from the multiplexer 5 into DC voltages and output the same. The DC voltage are used to drive a tachometer 9 to display the rpm of the engine. The DC voltages are further sent to a V-F converter 10, a frequency divider 11 and a monostable circuit 12 and output as positive pulses. The positive pulses are sent to a counter to calculate and obtain the mileage.
In the above prior art, the output DC voltages are first used to drive the tachometer and then are converted into the frequency signals to enable the counter to calculate, the mileage. According to such arrangements, several shortcomings exist as follows:
1. The sin and cos coordination coils of the speedometer will generate heat to bias the voltage of the IC and affect the accuracy. PA1 2. The error of the speedometer resulting from the temperature difference or mechanical vibration must be first adjusted by a variable resistor so as to zero the speedometer. Such adjustment will lead to change of the output DC voltage and affect the mileage calculation of the odometer counter. As a result, the obtained mileage will be inaccurate.